It is common that a reinforcing glass fiber to be used to increase the strength or durability of various rubber products such as rubber tires or rubber belts including timing belts, is coated with a membrane formed by a rubber type treating agent in order to increase the adhesion between the glass fiber and a rubber base material in a rubber product and in order to increase the durability of the rubber product by protecting the glass fiber itself. As such a rubber type treating agent, a water-soluble treating agent comprising a condensate of resorcinol with formaldehyde, and a rubber latex, as the main components (hereinafter sometimes referred to as “RFL treating agent”), or a treating agent having a rubber composition dissolved in a solvent (hereinafter sometimes referred to as “rubber cement”), is known.
Further, the above glass fiber for reinforcing rubber products is commonly produced by a producing method which includes the following processes (A) to (C).
(A) A process of drawing together some of glass fiber strands obtained by bundling many glass filaments while applying a sizing agent thereto, followed by drying, and impregnating an RFL treating agent thereto, and then, solidifying the RFL treating agent impregnated to the glass fiber strands, to form a coating layer thereby to obtain a coated glass fiber.
(B) A process of subjecting the coated glass fiber to twisting to form a twisted yarn.
(C) A process of putting at least two twisted yarns together to form a plied yarn.
Further, in order to increase the adhesion between a reinforcing glass fiber and a rubber base material in a rubber product, it is common to further include the following process (D) in addition to the above processes (A) to (C).
(D) A process of coating a rubber cement on the surface of the plied yarn, and then, solidifying the rubber cement applied on the plied yarn to form a coating layer.
Here, the glass fiber strand used in the above process (A), is one prepared by bundling from 200 to 2,000 glass filaments having a diameter of from 3 to 10 μm. Further, it has been common to draw a plurality of such glass fiber strands together and to impregnate an RFL treating agent thereto.
That is, in the following Patent Document 1, it is disclosed that a high-strength glass strand prepared by bundling from 200 to 2,000 high-strength glass filaments having a diameter of more than 8 μm and at most 10 μm, is used, and 1 to 10 such high-strength glass fiber strands are drawn together and are continuously introduced into the RFL treating agent and impregnated therewith.
Further, in the following Patent Document 2, it is disclosed that a high-strength glass fiber strand prepared by bundling from 200 to 2,000, preferably from 300 to 600, high-strength glass filaments having a diameter of from 3 to 6 μm, is used, and from 1 to 10, preferably from 1 to 6, such high-strength glass fiber strands are drawn together to form a primary yarn of a specific yarn count, composed of from 200 to 5,000, preferably from 800 to 2,000, high-strength glass filaments, whereby a coated layer made of the RFL treating agent is formed on the surface of the primary yarn.
Further, in the following Patent Document 3, it is disclosed that a high-strength glass fiber strand prepared by bundling from 500 to 800 high-strength glass filaments having a diameter of from 6 to 8 μm, is used, and from 1 to 8 such high-strength glass fiber strands are drawn together.
Further, the following Patent Document 4 discloses a treating method of a glass fiber wherein a strand having glass fiber filaments drawn together or a group of such strands, is immersed in a treating agent, and then, it is passed through at least one die to squeeze and impregnate the treating agent. Further, the excess treating agent on the surface of the above glass fiber is removed by at least one pair of rollers.
Patent Document 1: JP-A-11-217739
Patent Document 2: JP-A-11-158744
Patent Document 3: JP-U-1-111848
Patent Document 4: JP-A-9-25141